Tracer incendiary materials including liquid alkylaluminum and compatible inorganic oxidizer

ABSTRACT

AN ALKYLAUMINUM-BASED MATERIAL SUITABLE FOR TRACER APPLICATIONS HAVING A LOWER ALKYLUMINUM COMPOUND SUCH AS TRIETHYLALUMINUM OR MIXTURE THEREOF, AN INORGANIC OXIDIZER, AND OPTIONALLY A FINELY DIVIDED METAL OR METAL HYDRIDE.

United States Patent i 3,788,907 TRACER INCENDIARY MATERIALS INCLUDINGLIQUID ALKYLALUMINUM AND COMPATIBLE INORGANIC OmIZER U. AlbertLehikoinen, Detroit, Mich., assignor to Ethyl Corporation, Richmond, Va.No Drawing. Filed Sept. 7, 1972, Ser. No. 287,068 Int. Cl. C06d 1/10 US.Cl. 149-22 19 Claims ABSTRACT OF THE DISCLOSURE An alkylaluminum-basedmaterial suitable for tracer applications having a lower alkylaluminumcompound such as triethylaluminum or mixtures thereof, an inorganicoxidizer, and optionally a finely divided metal or metal hydride.

BACKGROUND OF THE INVENTION This invention relates to materials Whichare suitable for use as the active ingredient in a tracer projectile.The invention relates to novel compositions which have the necessarycharacteristics to fulfill the special requirements of tracer materials.

Tracer ammunition (referred to hereinafter as tracers) is used to markthe flight of a bullet or projectile after firing from a weapon. Thus,the accuracy of fire directed at a target can be assessed and corrected,if necessary. However, special problems are encountered in tracersbecause the visible fiight path or tracer signature may also serve tolocate the gunners position. Thus, a short ignition delay is desirable.Other considerations of tracer materials involve eifect on ballistics ofthe projectile, burning time length, rate of burning, light intensityand muzzle flash. The muzzle blast or flash when firing tracers shouldnot be brighter than ordinary and should avoid blinding the gunnertemporarily, as well as marking his location. The light intensityrequired should be sufiicient to enable the flight path of theprojectile to be marked at distances of from several hundred to Wellover thousands of yards depending on the type of weapon being fired. Therate of burning should be fast enough to obtain good combustion but slowenough to burn throughout the flight of the projectile. Thus, the idealagent should have a short ignition delay, a fast burning rate andconsiderable flaring.

Previous tracer materials have contained a metal and an oxidizer with asuitable amount of resin or polymeric binder. Several recipes for tracerformulations can be found in Military and Civilian Pyrotechnics, Ellern,Chemical Publishing Co., New York, 1968, pp. 362-365. According to Dr.Ellern, page 129, tracers are very small flares pressed into a cavity atthe base of a small-arms or artillery projectile. They must be able towithstand high pressures without igniting and yet ignite very shortlyafter being fired from. the weapon.

The object of this invention is to provide a novel tracer compositionbased on alkylaluminum compounds. Another object of this invention is toprovide a tracer with short ignition delay, fast burning rate andconsiderable flaring. Another object of this invention is to provide atracer material which is self-igniting but safe to handle and store.These and further objects will become apparent from the followingdescription of the invention.

3,788,907 Patented Jan. 29, 1974 SUMMARY OF THE INVENTION Accordingly,the foregoing and other objects of the invention are met by providing acomposition suitable for use as a tracer material, said compositioncomprising (a) an alkylaluminum compound having not more than about 4carbon atoms in each alkyl radical attached to the aluminum, and

(b) an inorganic oxidizer.

Preferable alkylaluminum compounds are triethylaluminum,trimethylaluminum, and mixtures of these. The inorganic oxidizer can beany inorganic oxidizing agent compatible with the alkylaluminum; andreferably is an oxygen-containing compound of sodium or strontium. Themost preferred inorganic oxidizers are sodium chlorate and strontiumperchlorate, although a number of other compounds are satisfactory. Inanother aspect of this invention is provided a three component tracermaterial. Specifically, it is a composition suitable for use as a tracermaterial comprising (a) an alkylaluminum compound having not more than 4carbon atoms in each alkyl group attached to the aluminum,

(b) an inorganic oxidizer, and

(c) a metal or metal hydride in finely divided form.

The foregoing preferred alkylaluminums and inorganic oxidizers are alsoapplicable to this tracer composition. Moreover, the metal compoundpreferably employed can be either a metal, such as magnesium, aluminumor boron, or a metal hydride such as zirconium hydride or lithiumaluminum hydride.

DESORIPT ION OF PREFERRED EMBODIMENTS A preferred embodiment of thisinvention is a composition suitable for use as the active material in atracer projectile, said composition comprising an alkylaluminum compoundhaving not more than 4 carbon atoms in each alkyl radical and aninorganic oxidizer. The alkylaluminum compound of these tracercompositions can be any alkylaluminum which is capable of independentignition when exposed to atmosphere. Generally, the lower alkyl groupsattached to aluminum provide an alkylaluminum sufficiently active toself-ignite upon short exposure to the atmosphere. By the term loweralkyl is meant alkyl radicals having not more than 4 carbon atoms ineach alkyl radical attached to the aluminum atom. Thus, preferredalkylaluminum compounds are those having lower alkyl groups. Typical ofthese are methyl, ethyl, propyl, and butyl groups. Therefore, preferredalkylaluminum compounds are trimethylaluminum, triethylaluminum,trin-propylaluminum, and tri-n-butylaluminum. Isomeric forms of thepropyl and butyl groups are also typical such as tri-isopropylaluminum,tri-isobutylaluminum, and tritert-butylaluminum. Mixtures of thesecompounds and of the alkyl groups such as triethylaluminum/trimethylaluminum, triethylaluminum/tri-n-propylaluminum, and the like, anddiethylmethylaluminum, dimethylethylaluminum, diethylpropylaluminum,diethyl-tert-butylaluminum, methylethylpropylaluminum, and the like aretypical. The hydrides are also examples of alkylaluminum compoundstypical of this invention and such compounds as diethylaluminum hydride,diisobutylaluminum hydride, ethylmethylaluminum hydride, and the likecan be used. The

alkylaluminum halides may also be employed in this invention. Typical ofthese are diethylaluminum chloride, ethylaluminum dichloride,methylaluminum sesquichloride, ethylaluminum sesquichloride, and thelike.

When using a mixture of alkylaluminum compounds, such astriethylaluminum and trimethylaluminum, it should be recognized that acertain amount of disproportionation of the alkyl groups may occureither during manufacture or on storage. Thus, it may be diflicult toexactly pinpoint the composition at any particular time when usingmixtures of alkylaluminum compounds. To rectify this, the finalcomposition is always referred to by the amount and type of materialsoriginally included.

The amount of alkylaluminum compounds used in the tracers should besufficient to cause ignition readily and to sustain a rapid burningrate. Typically from at least about percent by weight to about 60 weightpercent of the total composition is the alkylaluminum compound. Ofcourse, the best amount of alkylaluminum to use will vary depending onthe other components of the tracer material and the particularalkylaluminum compound used. However, below about 15 weight percentthere is not suflicient material to sustain burning for the entireflight of a projectile and to initiate combustion. On the other hand,above about 60 weight percent the tendency is to intensify the muzzleblast effect of the weapon without sufiicient ignition delay to providefor a satisfactory tracer signature. Preferably, the alkylaluminumcompound is present at from about 40 weight percent to about 60 weightpercent. Most preferably the alkylaluminum compound is an equimolarmixture, that is to say, a 50:50 mole percent mixture oftrimethylaluminum and triethylaluminum at from about 40 to about 60weight percent of the total composition.

The oxidizer is present because sufficient oxygen to maintain combustionmay not be present in the cavity of the projectile. Traveling at greatspeed, a partial vacuum is created behind the projectile as it movesthrough the air and not enough oxygen can get to the tracer to continuethe combustion started on firing. Hence, if an oxidizer was notprovided, the combustion would cease and the tracer go out prior toreaching the target.

The oxidizer of this invention must be compatible with thealkylaluminum, that is, it must be capable of being mixed with thealkylaluminum without reacting until the proper time. Nevertheless, itmust, on ignition of the alkylaluminum, decompose easily and rapidly toprovide sufficient oxidizing agent to continue combustion. Organicoxidizers and some inorganic oxidizers react with alkylaluminumcompounds. It is easy to test for this interaction by simply mixingsmall quantities of the oxidizer and alkylaluminum together in an inertatmosphere. Any evidence of reaction, such as increase in temperature,sparks, smoking or ignition eliminates the particular oxidizers.Therefore, the oxidizer of this invention is preferably an inorganicoxidizer which is compatible with alkylaluminum compounds, that is, onewhich is substantially inert when mixed with alkylaluminum compoundsunder anhydrous conditions in an inert atmosphere. Without limiting theinvention, it has been found that such inorganic oxidizers aresubstantially insoluble in alkylaluminum compounds. In other words, theytend to form physical mixtures when blended with alkylaluminumcompounds. Typical of compatible oxidizers are certain oxygen-containinginorganic oxidizers called per compounds. For example, peroxides,perchlorates, perchromates, permanganates, periodates, and the like aretypical. Also, some inorganic nitrates and oxides are compatibleinorganic oxidizers. More preferred inorganic oxidizers which arecompatible with alkylaluminum compounds are selected from alkali metaland alkaline earth metal compounds. Either alkali metal or alkalineearth metal compounds alone can be suitable inorganic oxidizers bythemselves or as mixtures. Typical are sodium nitrate, sodium chlorate,sodium iodate, sodium chromate, sodium peroxide, potassium nitrate,potassium chromate, potassium dichromate, potassium permanganate,strontium peroxide, strontium nitrate, strontium perchlorate, bariumperoxide, barium nitrate, and the like. Most preferable inorganicoxidizers compatible in the tracer material are sodium chlorate andstrontium perchlorate. Without limiting the invention to the alkalimetal and alkaline earth metal compounds, it should be recognized thatother inorganic oxidizers are compatible with the alkylaluminum-basedtracer materials of this invention; such as, copper oxide, manganeseoxide, boron oxide, for example.

The inorganic oxidizer should be present in an amount suflicient toprovide oxygen or other oxidizing agent to sustain combustion of thetracer material. Of course, this will vary because of the flightcharacteristics of the projectile, since some projectiles tumble endover end in flight and present only small oxygen ditficiencies, and theamount and type of alkylaluminum and other components in the tracermaterial. Generally speaking, the weight of inorganic oxidizer should befrom at least about 40 weight percent to about weight percent of thetotal tracer ma terial Weight. Preferably, the inorganic oxidizer shouldbe present in an amount of from about 40 to about 60 weight percent ofthe tracer material.

Therefore, a preferred embodiment of this invention is a compositionsuitable for use as the active material in a tracer projectile, saidcomposition comprising an alkylaluminum compound having not more than 4carbon atoms in each alkyl radical and an inorganic oxidizer. A morepreferred embodiment is the above composition wherein the alkylaluminumcompound is present at from at least about 15 to about 60 percent byweight and said inorganic oxidizer is present at from at least about 40to about 85 percent by weight; all percentages based on the total weightof the active material.

In some instances it is preferred to add, as a third component, a metalor metal compound or mixtures thereof to the tracer formulations of thisinvention. While massive metals themselves would not, except in 'veryspecial cases, lend themselves to use in tracer materials, it is knownthat finely divided metals ignite and burn intensely. This propertymakes a number of metals extremely advantageous to use in finely dividedform as a component of tracer materials. Preferably, a metal or a metalhydride is suitable in the tracers of this invention, and more preferredare a metal or a metal hydride when used in finely divided form. Themetal need not be so fine as to cause dusting, sticking, or otherhandling problems; but the particle size should be sufiiciently small tooxidize easily, rapidly, and with intense light being given off. Ofcourse, the metal is not critical so long as it meets the requirementsset forth above. Finely divided iron, copper, steel, magnesium,aluminum, boron, silicon, selenium, tellurium, titanium, zirconium,lead, manganese, tungsten, zinc, and the like are illustrative examplesof suitable metals. More preferred for inclusion in tracer materials aremetals selected from magnesium, aluminum, and zirconium. Most preferredis finely divided or powdered magnesium.

Not only are the metals themselves suitable, but in addition metalcompounds such as the hydrides and complex metal hydrides are suitablefor the tracer materials of this invention. For example, titaniumhydride, zirconium hydride, lithium aluminum hydride, boron hydride,sodium borohydride, sodium hydride, sodium aluminum hydride, calciumhydride, and the like are illustrated of typical metal hydrides andcomplex metal hydrides. Zirconium hydride is a preferred metal hydride.Without limiting the invention to the foregoing metal compounds, itshould be clear that any metal compound which is readily decomposable orwhich provides a highly active form of the metal for oxidation or whichis normally susceptible of the drastic oxidation in combustion and notmerely oxidative degradation over a prolonged period would be suitableas a component of the tracer material of this invention.

The metal or metal compound can be normally present in amountssufficient to add a bright, intensive flaring to the tracer combustion.Without limiting the invention, when the metal or metal compound ispresent in an amount of at least about 30 to about 75 weight percent ofthe total tracer material, a suitable tracer material is produced.Preferably, the metal is present at from about 45 to about 60 weightpercent of the tracer material.

Therefore, another preferred embodiment of this invention is acomposition suitable for use as the active material in a tracerprojectile, said composition comprising an alkylaluminum compound havingnot more than 4 carbon atoms in each alkyl radical, an inorganicoxidizer, and a metal or metal hydride or mixtures thereof in finelydivided form. The alkylaluminum compound can be any alkylaluminumcompound hereinabove described. However, the amounts required are not asgreat as in the two component system. Preferably from about 5 to about60 weight percent of the total weight of the active material can bealkylaluminu-m; more preferably from at least about .10 to about 30weight percent should be used. Similarly, the inorganic oxidizer is alsoas hereinabove described. Again, the amounts required are not so greatand preferably from at least about to about 40 percent by weight andmore preferably from about 20 to about 30 percent by Weight based on thetotal weight of material may be used. Thus, in a more preferredembodiment of this invention the active material for a tracer projectilecomprises from at least about 5 to about 60 percent by weight of analkylaluminum compound having not more than 4 carbon atoms in each alkylradical, from at least about 10 to about 40 percent by weight of aninorganic oxidizer, and from at least about 30 to about 75 per cent byweight of a metal, metal hydride, or mixture theerof in finely dividedform.

In addition to the foregoing, various other components may be added tothe tracer material of this invention. For example, binders, coloringagents, ignition-delay enhancers, destruct devices, light intensifiers,and the like may be used to produce a better tracer material or improveits properties. Without limiting the invention, typical binders arethose which when added to the tracer material cause stiffening of thematerial and increase its cohesion, While at the same time altering theburning characteristics little, if any. Typically, the binder may be anatural or synthetic polymer or gelling agent; for example, polyolefins,such as polyethylene, polypropylene, and polyisobutylene, paraffin Wax,high molecular weight polyethers, and the like.

Various coloring agents can also be used in the tracer materials of thisinvention without departing from the scope thereof. Basically, thecolors red and green are produced by the elements strontium and barium,respectively, usually as their realtively volatile chlorides. They areusually present either as the perchlorates or their less hazardousnitrate forms are used in conjunction with a halogen donor such asinorganic metal salts, such as sodium, barium, strontium, and calciumchlorides and the like. Copper powders may be added to formulasproducing green light as an intensifier. Yellow may be produced by thestrong tinctorial powder of sodium, for example, as with a sodium salt.Blue may be produced by including copper in the presence of chlorine (inits absence green is produced).

The use of additional pyrotechnic or explosive devices in tracermaterials is convenient because the tracer usually burns in cigarettefashion and thus serves as a delay for the later ignition of theexplosive. Operating in this manner the tracer may destroy theprojectile after a definite interval.

The tracer materials of this invention can conveniently be prepared bysimply mixing the dry ingredients together and then adding the liquidcomponents thereto forming a pasty mass which can be shaped as desired.The entire operation of mixing should be carried out under an- 6 hydrousconditions in an inert atmosphere, such as for example, under a nitrogenblanket.

The method or order of mixing the materials is not considered critical.Thus, the inorganic oxidizer may be added to the alkylaluminum, but forconvenience it appears easier to blend the liquid alkylauminum compoundinto the oxidizer. When a metal or metal hydride is used, it ispreferred to blend the oxidizer and metal or metal hydride and then addthe alkylaluminum. The resultant tracer material may range from a pastymass to particles of a solid depending on the type and amount of thevarious materials used.

The materials may be admixed at any convenient temperature althoughextreme temperatures should generally be avoided. The tracer materialcan be formulated conveniently at room temperature or at any temperaturebelow which the inorganic oxidizer is substantially insoluble in thealkylaluminum.

In practice the tracer material can be premixed and packed into theprojectile cavity or the cavity can be partially filled with the properamount of premixed dry ingredients and the desired amount ofalkylaluminum added to the cavity. Also, the entire premixed tracermaterial can be extruded into the cavity. When filling the cavityprecautions should continually be observed to avoid air and water, untilthe cavity is appropriately sealed.

The seal is important because its function is to prevent prematureexposure of the tracer material to the atmosphere and, thus, preventundesirable ignition. In another sense, however, the seal is notcritical to this invention in that any nonpermeable membrane which isinert to the tracer material, provides suitable storage life, ruptureseasily, or is ejected on firing the projectile and does not interferewith the pyrotechnical aspects of the tracer may be convenientlyemployed. For example, sealing membranes such as aluminum foil, viton,and Teflon are typical, but non-limiting illustrations.

The following examples serve to illustrate the tracer compositions ofthis invention.

EXAMPLE 1 ABLE l.-OOMPATIBILITY OF OXIDIZING AGENTS WITHTRIETHYLALUMINUM Compatible Not compatible N03, NaClOa, NaIOa,Nit-actor, Nazoa, K104, FeCl; KClOa, NaF, KNOz, moro Krono KMnOr, 5330., 16114010.,

Similar results are obtained when the alkylaluminum used forcompatibility testing is trimethylaluminum, an equimolar mixture oftriethylaluminum and trimethylaluminum, tripropylaluminum,tri-n-butylaluminum, and the like.

The burning characteristics of compatible systems were qualitativelytested for ignition delay, burning rate, and flaring by exposing thecompatible compositions of Table l to the atmosphere. Comparativeobservations of ignition delay were rated as long, average, or short.These terms are used to mean a delay of about 3 to 10 seconds, about 1to 3 seconds, and less than 1 second, respectively. The burning rate wascompared and the results reported as slow, average, and fast. As used inthis application, these terms mean arate of about 5 to 15 seconds, about2 to 5 seconds, and less than 1 to 2 seconds respectively. The flaringcharacteristics of the compositions were rated visually as none, fair,bright, or very bright. The burning characteristics of compatiblecompositions are given in Table 2 as follows:

Agent Ignition delay Burning rate Flaring NaNOq NaIOs... NazCrO4.

Similar burning characteristics are observed when the alkylaluminumcompound used is trimethylaluminum, mixtures of trimethylandtriethylaluminum, tripropylaluminum, tri-n-butylaluminum, and the like.

From the results shown in Tables 1 and 2, it can be seen that a widevariety of oxidizing compounds may be used in the tracer materials ofthis invention. Preferred tracer compositions are prepared from sodiumperoxide and sodium chlorate with triethylaluminum. Most preferred isthe system comprising triethyaluminum and sodium chlorate.

Tracer formulations containing an equimolar mixture of triethylaluminumand trimethylaluminum are especially preferred. While other mixtures canalso be used, a tracer having shorter ignition delay than eitherindividual component alone is conveniently prepared from 50 mole percentof triethylaluminum and 50 mole percent of trimethylaluminum. Typicalformulations having such an equimolar mixture are given below:

56 weight percent NaClO in 50:50 mole percent TEA/TMA 56 weight percentNaClO in 50:50 mole percent TEA/ TMA thickened with 5.5 weight percentof Oppanol B200 In another formulation, a metal or metal hydride wasadded to a tracer formulation comprising triethylaluminum and eitherNaClO or Na O The procedure for this is shown in the followingillustrative example.

1 TEA: triethylaluminum TMA trimethylaluminum. A trademark of BadischeAnilinand Soda-Fabrik, for a commercially available form ofpolyisobntylene.

8 EXAMPLE 2 In a nitrogen box was cautiously blended 3 grams of NaClOand 2 grams of powdered magnesium. To this mixture were added 2 m1. oftriethylaluminum; the pasty mass was sealed in a glass vial and thenexposed to the atmosphere by breaking the vial in a suitable testlocation. The burning characteristics, according to the ratings forTable 2, were observed and recorded. The results of exposing theformulation prepared in Example 2 and of several other formulationsprepared in the same manner are given in Table 3.

TABLE 3.BURNING CHARACTERISTICS OF SYSTEMS CONTAINING TRIETHYLALUMINUM,AN OXIDIZING AGENT, AND METAL OR METAL HYDRIDE Agents Ignition delayBurning rate Flaring NaClO:iZrH: Long Fast Bright. NaClOsAl .-do "do Do.NaClOz-Mg Short Very iast* Very bright. NaCl0aB..- Fast..- Bright. NaO1OT.i Al'Fl'i Avera e (In Do. NazO2ZrH2 rin (in D0. NazOz-Al d0 .d0 D0-NfizOz-Mg d0 D0- NfizOa-B dO DO. N 8202-LiAlH4 .do Slow Fair.

*Very iast=Faster than one second by an order of magnitude.

Similar results can be obtined when the alkylaluminum compound used istrimethylaluminum, an equimolar mixture of triethylaluminum andtrimethylaluminum, tripropylaluminum, tri-n-butylaluminum, and the like.Further, similar results can be obtained when the inorganic oxidizer ispotassium dichromate, potassium permanganate, strontium peroxide, bariumperoxide, and the like.

The formulations of Table 3 all produce a yellow light when burned. Asuitable tracer formulation producing red light can be prepared by usinga strontium compound as the inorganic oxidizing agent, for example,

43 weight percent SrO 29 weight percent powdered Mg;

and 28 weight percent triethylaluminum 43 percent Sr(NO 29 weightpercent powdered Mg;

and 28 weight percent triethylaluminum 43 weight percent Sr(ClO 29weight percent powdered Mg; and 28 weight percent triethylaluminum.

A bright-red, flare-like fire resulted from combustion of the aboveformulations. Similar formulations may be obtained when thetriethylaluminum is replaced with trimethylaluminum, mixtures oftriethylaluminum and trimethylaluminum, tripropylaluminum,tri-n-butylaluminum, diethylaluminum hydride, diisobutylaluminumhydride, and the like.

Using the procedure of Example 2, various formulations were prepared andtested. These illustrative examples are found in Table 4.

TABLE 4.-COMPOSITION AND COMBUSTION CHARACTERISTICS OF ALUMINUMALKYL-BASED TRACER FORMULATIONS Weight percent Total Example TEA/ wt.,Number Mg Zr NaClOe SI'(C10-l)2 TMA mg. Physical appearance Combustioncharacteristics 30 20 800 Paste; liquid completely absorbed. Brightyellow sustained flare. 25 15 800 do Dglayed ignition. Bright yellowsporadic are. 10 800 ...do No spontaneous ignition. 40 400 Solidssettled out, liquid on top Sporadic, spread-out yellow flare. 30 400..do Sporadic yellow flare. 20 400 do Sustained yellow flare. 20 800Liquid mostly absorbed by solids- Sustained light-yellow flare. 15 800Paste; liquid just absorbed Do. 10 800 .do Fast, light-yellow flash. 20800 Pasteliquid completely absorbed" Bright, yellow sustained flare. 20800 .do Delayedignition. Slightly sporadic bright,

yellow flare. 10 800 do No spontaneous ignition. 25 Spontaneousignition. Red flare. 20 Sporadic, very bright, red flare. 15 D0. 10 800.--.do N o spontaneous ignition. 40 400 Solids settled, liquid on topSporadic red flare. 400 -----do Do. 20 400 Paste; liquid absorbedSustained red flare. 20 800 do Two discrete sustained red flares. 15 800.....do Sustg itned flare, red at first turning to 10 800 .do Fast,light-red flash.

TEA/TMA is a 50:50 mole percent mixture of triethylaluminum andtrimethylaluminnm.

EXAMPLES 25-32 According to the procedure set forth in Example 2,suitable tracer formulations are prepared having the followingcompositions:

Weight percent of component Example number Mg Zr NBClOs Sr(ClO4)2 TEATMA TEA/TMA is a 50:50 mole percent mixture of trlethylaluminum and.trimethylaluminum.

EXAMPLE 33 In a nitrogen box under anhydrous conditions, a blend of 250mg. of powdered magnesium and 150 mg. of sodium chlorate was made in a x75 mm. test tube. A 5.56 mm. tracer projectile was placed nose down in aholder and 100 mg. of the blend was added to the tracer cavity. Thisblend filled the projectile to about 1/16 of an inch below the top ofthe cavity opening. Then 25 mg. of an equimolar mixture oftriethylaluminum and trimethylaluminum was added dropwise from acalibrated dropping pipette. The final mixture was 50 weight percentmagnesium, 30 weight percent sodium chlorate, and 20 weight percentTEA/TMA. A square of aluminum foil tape containing an acrylic adhesivewas cut to fit, placed over the cavity, and the corners pressed downalong the sides to seal the tracer material into the cavity. Theprojectile was removed from the holder, inverted in the nitrogen box,and left standing for 24 hours. After this time there appeared to be noleakage of the tracer material from the cavity.

The tracer formulations are useful in small arms, artillery,anti-aircraft and similar weapons. With very little modification theformulations may also be useful in devices for military and civiliansignalling applications, such as, flares, distress signals, and thelike. Other ap lications will be readily apparent to skilledpractitioners of military and civilian pyrotechnics.

The above description is illustrative and the invention should belimited only by the lawful scope of the following claims.

What is claimed is:

1. A composition suitable for use as the active material in a tracerprojectile, said composition comprising (a) a liquid alkylaluminumcompound having not more than 4 carbon atoms in each alkyl radical and(b) an inorganic oxidizer compatible with said alkylaluminum compound.

2. A composition of claim 1 wherein said alkylaluminum compound is atrialkylaluminum compound.

3. A composition of claim 2 wherein said trialkylaluminum istrimethylaluminum.

4. A composition of claim 2 wherein said trialkylaluminum istriethylaluminum.

5. A composition of claim 2 wherein said trialkylaluminum compound is amixture of triethylaluminum and trimethylaluminum.

6. A composition of claim 5 wherein said inorganic oxidizer is sodiumchlorate.

7. A composition of claim 5 wherein said inorganic oxidizer is strontiumperchlorate.

8. A composition of claim 1 wherein said composition comprises (a) fromat least about 5 to about 60 percent by weight of an alkylaluminumcompound having not more than 4 carbon atoms in each alkyl radical,

(b) from at least about 10 to about 40 percent by weight of an inorganicoxidizer compatible with an alkylaluminum compound, and

(c) from at least about 30 to about percent by weight of a materialselected from a metal, metal hydride, or mixtures thereof in finelydivided form.

9. A composition of claim 8 wherein said alkylaluminum compound is atrialkylaluminum compound.

10. A composition of claim 9 wherein said trialkylaluminum istrimethylaluminum.

11. A composition of claim 9 wherein said trialkylaluminum istriethylaluminum.

12. A composition of claim 9 wherein said trialkylaluminum compound is amixture of triethylaluminum and trimethylaluminum and said material is ametal.

13. A composition of claim 12 wherein said metal is selected from thegroup consisting of aluminum, magnesium, and boron.

14. A composition of claim 13 wherein said metal is magnesium.

15. A composition of claim 14 wherein said inorganic oxidizer is sodiumchlorate.

16. A composition of claim 14 wherein said inorganic oxidizer isstrontium perchlorate.

17. A composition of claim 8 wherein said alkylaluminum compound is amixture of triethylaluminum and trimethylaluminum and said material is ametal hydride selected from the group consisting of zirconium hydrideand lithium aluminum hydride.

18. A composition of claim 17 wherein said inorganic oxidizer is sodiumchlorate.

19. A composition of claim 17 wherein said inorganic oxidizer isstrontium perchlorate.

References Cited UNITED STATES PATENTS 3,441,455 4/1969 Woods et al14919 X 3,147,161 9/1964 Abere etxal 14919 CARL D. QUARFORTH, PrimaryExaminer E. A. MILLER, Assistant Examiner US. Cl. X.R.

